Spark gap for use more particularly in high-frequency ignition systems for internal-combustion engines



April 2, 1946. H. v. G. STUBBS 2,397,764

SPARK GAP FOR USE MORE PARTICULARLY IN HIGH-FREQUENCY IGNITION SYSTEMS FOR INTERNAL-COMBUSTIONENGINES Filed June 1, 1942 2 Sheets-Sheet 1 2 2 f g X ,1" m E j 7 IwvenZoh'.

" H, 1 G. ail/51M By A Zia/ways April 1946- H. v. e. s'ruBBs 2,397,764

SPARK GAP FOR USE MORE PARTICULARLY IN HIGH-FREQUENCY IGNITION SYSTEMS FOR INTERNAL-COMBUSTION ENGINES Filed June 1, 1942 2 Sheets-Sheet 2 I77V7Z for; h. Mada/51,6

2 I 7 tin/'7 59y;

Patented Apr. 2, 194a UNITED STATE SPARK GAP FOR USE MORE PARTICU-- l 1 LARLY IN HIGH-FREQUENCY IGNITION I SYSTEMS FOR INTERNAL-COIVIBUSTION enemas Harold Vivian George Stubbs, near Towcester, England, assignor to The Plessey Company Limited, Ilford, England Application June 1 1942, Serial No. 445,364

In Great Britain July 1, m

9 Claims.

, This invention relates to spark gaps of the type adapted with particular advantage for 'use in high-frequency ignition-systems for internal combustion engines; in such systems as is known a condenser is caused to discharge through a, spark gap in series with the primary winding of a transformer and dimculties are frequently found to arise from erratic'performance of the spark gap.

It has now been discovered that calcium fluoride has a remarkable stabilising eifect on the breakdown of such gaps and one characteristic feature of the invention consists in theprovision of this material in the gap proper or in one or more of the parts of the device by which the gap is confined. With great advantage the calcium fluoride is used in the form of a loose powder in the gap proper but it may alternatively or in addition if desired be embodied for example in J the material of one or both electrodes... Our investigations have shown that in a tube containing calcium fluoride in the gap in powder form sputtered metal from the electrodes is cleaned up mechanically and does not deposit on the glass to any serious extent whereas in a tube which has no such powder in the gap sputtered metal does deposit on the glass and soon causes erratic results. Under these conditions the breakdown Voltage (commonly referred to as the startin v voltage) fluctuates, discharges take placevfrom the electrodes to the deposit on the glass, and the device becomes useless for the purpose required. The presence of powder in the gap would atmospheric pressure or argon by the presence of seem to have the effect that the powder is mainwhich we believe the tendency to sputtering can be further reduced.

The electrodes may conveniently be discs of nickel or nickel alloy mounted on metal supports spaced apart by insulating material, use being made of suitable gas-tight seals. Alternatively th gap may be hermetically sealed in a vitreous or ceramiccontainer. If it is desired to incorporate the calcium fluoride in one or both electrodes use may be made of any of the well-known methods of powder metallurgy. For example, finely divided nickel may be ball-milled with approximately 10% of calcium fluoride for fortyeight hours, and the resulting mixture pressed into a compact at about 20 tons per square inch,

the compact being then sintered at a temperature of 950 C.

According now to a further feature of thein as nitrogen, the capillary tube connecting to a suitable aperture or passage in the body of the spark gap. This arrangement may be used whether or not calcium fluoride is employed; when calcium fluoride is employed it is not placed in the reservoir although some may diffuse therein by way of the capillary tube during operation.

The invention will now be more fully described by reference to the examples illustrated in the accompanying drawings in which the same reference numerals have been adopted to indicate the same or analogous parts.

Fig. l is an elevational view and Fig. 2a longitudinal axial section on the line X-X of Fig. 1 of one constructional form of the spark gap device;

Fig. 3 is a cross section on the line Y-Y of Fig. 1; and

Fig. 4 illustrates in partial section on an en-j larged scale one end portion of the view shown in Fig. 2;

Fig. 5 represents the combination of a spark.

gap as above referred to with a gas supply arrangement according to this invention;

Fig; 6 is a transverse section of the arrangement taken on the line Y--Y of Fig. 5 the gas reservoir shown in these figures being deemed to' frequency ignition system.

As represented in the Figs. 1 to 4 the device comprises a glass tube l'of cylindrical cross section which is closed at each end by a'cap twhich "caps are constructed to carry the supports for the electrodes proper 3 and consist preferably of copper. The electrodes 3 are copper rods the inner ends of which are adapted to carry the eleg: trode material 4 here shown in the form of discs which may be of nickel or nickel alloy. The caps 2 are connected to the ends of the tube I by copper glass seals 5 as indicated more particularly in Fig. 4. The reference 8 indicates the charge of calcium fluoride powder, I are theconnecting terminals and 8 is the interior containing air or a gas such as nitrogen or argon at atmospheric pressure. The calcium fluoride powder used with advantage is of a fineness which will pass easily through a 200 mesh sieve when it will be found fine enough to be blown into the sparking space during the operation of the gap. The sealing of the copper electrode supports 2 to the glass tube I may be effected by any well known method. I

As regards the calcium fluoride it is recommended to use .2 gram of approximatel 200 mesh powder in one spark tube of a capacity of about 5 cc.

As already pointed out the calcium fluoride is with advantage used in the gap in the form of a fine powder with the apparent effects already referred to, particles, of nickel being readily detectable in the calcium fluoride under the microscope in spark tubes provided with nickel electrodes. It is obvious, however, that this material may if desired be embodied instead in one or more of the metal constituents .of the device such as preferably one or 'both electrodes by which the spark gap proper is confined, or as likewise already pointed out calcium fluoride may be used both in powder form in the gap proper and in one or both of the electrodes or other parts of the device and the atmosphere of the gap itself may be air or a gas such as preferably nitrogen or argon.

Now as shown in Figs. 5, 6 and '7 the spark gap again consists of a glass tube I closed at both ends by caps 2 which are constructed to carry the electrode supports 3 and preferably consist of copper. The electrode supports 3 which preferably are integral with the caps 2 are copper rods supporting the electrode material 4 again preferably in the form of discs of nickel or nickel alloy. The connection between the tube I and Fig. 8 represents by way of example one of the usual circuits showing the arrangement of the spark gap I therein in which SI indicates a source of EMF which may be an alternator or magneto, C the condenser P, the primary of a high freconnected in the usual manner to the distributor D. of. the high frequency ignition system. The

spark gap is caused to flash when the potential whether direct current or alternating is of a predetermined value above earth dependent upon the distance between the spark electrodes. When this occurs as is well known high frequency oscillations are produced determined by the values of the capacity of the condenser C and the inductance in series therewith. These high frequency oscillations are induced into the secondary S from primary P and from there to the distributor D.

It will be obvious to those skilled in the art that the invention would not be held to be limited to its use with either a spark gap construction or to a gas supply arrangement as hereinbefore particularly described but should be deemed to include spark gaps of any construction which can be readily adapted for the useful embodiment therein of calcium fluoride in any of the forms referred to or for its association with a gas supply of the type illustrated herein.

the caps 2 is effected in any known manner but preferably by copper-glass seals. The sparking gap proper between the electrodes and the interior space 8 of the tube are according to this invention charged with an atmosphere of gas such as preferably nitrogen or argon the supply of which is maintained by the association of the spark gap tube with a gas reservoir as shown at I0 which may be of metal or as shown in Fig. 7. of glass. To this end according to Figs. 5 and 6 the metal reservoir I0 is connected with one of the caps 2 by means of a capillary tube 9 of metal which is soldered at one end into one of the 7 caps 2 and at the other end into the reservoir.

In Fig. 7 the capillary tube 9 consisting of glass is shown to be made in one both with the tubular body of this spark gap and with the gas reservoir itself. I are again the terminals of the device by means of which it is connected in the circuit of a high frequency circuit in any well known manner. 7

As already pointed outthis arrangement has been devised to provide and maintain the requisite gas supply for the gap with the advantages hereinafter mentioned but if desired the gap mayin addition contain calcium fluoride either. in

the form of a powder or embodied in-one or both electrodes or other metallic parts of the device;

ing a casing of insulating material and in the interior thereof in association withthe electrodes The gas reservoir will be found to have the chemical changes, e. g. temperature rise and dissociation, which occur in the spark gap.

calcium fluoride embodied in one of the metallic parts of the spark gap within said casing substantially as set forth.

3. A spark gap of the type described comprising a casing of insulating material, end closures for\ said casing in the form of metal caps, electrode supports' extendlng from said caps co-axially to the interior of the gap, electrodes carried by said supports and calcium fluoride embodied in said electrodes by incorporation therein by a powder metallurgical method substantially as set forth.

4. A spark gap of the type described comprising an external casing of glass, copper caps hermetically sealed to the ends of said casing, cop: per. electrode supports extending co-axially to the interior of said casing, nickel electrodes carried by said supports and forming between them a sparking space and a charge of calcium fluoride powder within the gap proper of a fineness adapted to be blown into said sparking space during the operation of the'gap substantially as set forth.

gas reservoir externally of said casing and means for establishing capillary communication between said reservoir and said casing substantially as set forth. I

' '7. A spark gap of the type described comprising an external casing of insulating material, metal caps hermetically sealed to the ends of said casing, electrode supports of copper extending coaxially to the interior or said casing, nickel electrodes carried by said supports, a reservoir for supplying gas such as nitrogen to the spark gap and a tube connecting said'casing and said gas reservoir to establish capillary communication between them.

8. A spark gap of the type described-compriscalcium fluoride embodied in metallic ing an external casing of insulating material, elecv trodes hermetically enclosed within said casing, a gas such as nitrogen in theinterior or said casing and a charge of calcium fluoride in the interior of said casins in the form of powder 01' a fineness adapted to be blown into the sparking space during the operation of the spark gap.

9. A spark gap of the type described comprising an external casing of insulating material, electrodes hermetically enclosed within said casing, a gas such as nitrogen within said casing-and parts within the interior 01 said casing by incorporation therein, substantially as set forth.

HAROLD VIVIAN GEORGE STUBBS. 

